Eggs are an important nutritional product. Whole hard cooked eggs continue to be popular in institutional food service and in retail marketing. Typically in large scale production of hard boiled eggs, uncooked shell eggs are cooked in water to a hard boiled level and then subjected to prompt cooling in a cold water bath for avoiding the formation of gray discoloration on the yolk followed by air cooling. After the cold water bath and air cooling steps, the egg shells are cracked and peeled by any one of a wide variety of egg shell peeling machines known in the art. However, peeling can be difficult to perform without at least some damage to the egg white albumen, without affecting the shape and texture of the hard boiled eggs, or without effecting their taste or appearance.
Despite their usefulness, egg peeling machines still yield a certain degree of non-uniformity of peeling. For example, while the large majority of the eggs are wholly peeled with the albumen fully intact, some eggs may still have portions of shell adhered to the cooked albumen. Still other eggs are missing portions of the albumen or yolk. In either case, the damaged eggs do not have the desired appearance and the potential yield of the egg peeling machine is decreased. One of the reasons this occurs is due to the strong adherence of the shell to the albumen via the membrane that otherwise ordinarily separates the two. Because such machines will inevitably result in a certain number of eggs that are not considered desirable for sale as whole cooked eggs, the desirable eggs need to be sorted by an operator from the undesirable eggs. The manual sorting can bottleneck the entire process and adds to the processing cost per egg. As the peeled eggs with an undesirable appearance are not suitable for retail sale as whole cooked eggs, they are typically set aside for less valuable uses such as chopped egg for salads.
Some have proposed that the problem of overly strong adherence of membrane to albumen is exacerbated in freshly laid eggs versus aged eggs. Thus, instead of allowing the eggs to age before boiling and shelling, some, such as U.S. Pat. Nos. 3,216,828 and 5,053,238, have proposed to artificially age the eggs by hastening the loss of CO2 or dissolving or softening the shell by a chemical treatment. However, such chemical treatments can potentially alter the flavor, odor, and coloration of hard boiled eggs. Moreover, many consumers desiring more wholesome foods are put off by chemical treatment of foodstuffs.
Others, such as U.S. Pat. Nos. 3,603,243 and 3,684,531, have proposed freezing a portion of the egg after boiling followed by cracking of the shell while the portion is still frozen. However, the freezing of a hard boiled egg can cause them to become tough and watery. Additionally, contrary to the teachings in these patents, we have found that it is actually more difficult to peel an egg whose outer portion has been frozen since the egg shell adheres too tightly to the albumen. As a result, peeling results in removal of some of the egg white.
Thus, there is a need to improve the yield and throughput of egg peeling machines and lower the overall processing cost without sacrificing appearance, flavor or odor, or requiring the use of a chemical treatment.